Meta-analysis of 87 tDCS studies correlating tDCS electric fields and performance to working memory

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In this article, “Identifying regions in prefrontal cortex related to working memory improvement: a novel meta-analytic method using electric field modeling”, 87 tDCS studies on working memory performance were analyzed. Based on this analysis, the authors created an optimized montage targeting the lower DLPFC (dorsolateral prefrontal cortex).

tDCS uses a low direct current to stimulate the brain. In past research papers, tDCS has been shown to have the potential to alter brain function. In this review, we will be discussed the effects that tDCS has on working memory (WM). As referenced, “WM deficits are observed in neuropsychiatric disorders, including major depressive disorder, schizophrenia, and obsessive-compulsive disorder (Gold et al., 2019; Heinzel et al., 2018; Marraziti et al., 2010).” This important statement helps to outline the need to understand the effects of tDCS on WM.

The paper goes on to state that over the large number of studies done on the effect of tDCS on working memory, there are many variations as to the electrode placement and intensity that were used. “For example, to improve WM performance, several studies opted to place the anode over F3 (according to the 10-10 system), in order to target the dorsolateral PFC (DLPFC). However, other studies have used slightly different targets, such as F5 or F7 to stimulate more ventro-lateral portions of the PFC, corresponding to the inferior frontal cortex (IFC) (Di Rosa et al, 2019, Weintraub-Brevda & Chua, 2019).” The picture on the right shows both the 10/20 and 10/10 electrode placement maps. These maps are internationally recognized and the standard for referencing different locations on the head. They are the same maps, with the 10/10 reference (B) showing the same positions in (A) as well as the ones between them.

Upon comparison of the results of the 87 studies, the authors checked the effects of stimulation of the left DLPFC (F3) versus the right DLPFC (F4). As expected, and shown in the research, stimulation of the right DLPFC (F4) did not have noticeable effects on improving WM. However, stimulation over the left DLPFC (F3) did show improvements in WM compared to a control group. Interesting to note that it is this same left DLPFC that is targeted by headsets such as LIFTiD, Flow, and PlatoScience.

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